Water is a primary transmission vector for the spread of potentially dangerous microorganisms. It is also an excellent growth medium for certain kinds of molds and algae causing unwanted discoloration and turbidity in the water. Some of the organisms that will grow in standing water include Chlorococcum, Chlorella, Cledaphora, Microcystis, Osciliatoris, Spirogyra, Ulaothrix, Vanetteria and the fungus Aspergillus flavus. Thus, the prevention or inhibition of growth of potentially harmful microorganisms in water has been a longstanding problem. This is especially true where there is extensive human contact with the water as in bathing or in recreational areas such as swimming pools.
The most common prior art method of water treatment for microorganisms has been to treat the water with halogens such as chlorine. One way of doing this is to inject elemental chlorine directly into the water, usually as the water is being filtered. Although chlorine is an excellent water treatment agent, it has several inherent problems One of the major problems is that it is difficult to maintain the necessary concentration of chlorine in the water to be effective. Chlorine that is dissolved in water will gradually escape in gaseous form. This loss of soluble chlorine is accelerated in direct sunlight. Thus, when using this conventional water treatment method, it is necessary to continuously replace the lost chlorine. Another disadvantage of using elemental chlorine is that it forms hydrochloric acid as it dissolves in the water. This causes a drop in the pH of the water and makes acid-base balancing difficult. Thus, when using chlorine as a water treatment agent, it is also necessary to add a buffer system to the water in order to maintain the proper pH.
Chlorine may also be added directly to water as a powder as a hypochlorite such as sodium hypochlorite. When hypochlorites are dissolved in water, an equilibrium is set up between free chlorine and hypochlorous acid. The active ingredient is the elemental chlorine that is liberated in the equilibrium reaction and is therefore subject to the same problems as outlined above for free elemental chlorine.
Another method of controlling water-borne microorganisms is through the use of halogen substituted organics such as trichloro-S-triazinetrione and bromochlorodimethylhydantoin. This class of water treatment agents do not dissipate as rapidly as elemental chlorine and are much earier to handle and to store. However, they are quite expensive and a buffering system is still required to maintain a proper pH.